ADM-860C 04/14/0846
11.0 FLOWHOOD OPERATING PROCEDURE
The meter handle should be removed from the AirData Multimeter by unscrewing the captive fasteners on the
sides. The meter is inserted into the recess in the FlowHood base, using the captive fastener inside the base
to secure it. The two pneumatic tubes from the flow sensing grid attach to the pneumatic inlets on the meter.
The tube from the top side of the grid connects to the positive (+) pneumatic inlet on the meter; it is very important
that these connections are not reversed, since this will cause false flow measurements. The FlowHood flaps plug
inserts into the flaps receptacle on the back of the meter.
The thumbswitch plug connected to the handgrip is inserted into the external read jack on the left side of the
meter. The TemProbe sensor plugs into the temperature input jack on the back of the meter through the cutout
designed into the FlowHood base.
CAUTION: Avoid possible damage by removing all three electrical connections and both pneumatic connections
before removing the meter from the FlowHood base.
Turn the meter on. The display will then read FLO-HOOD, followed by CF: READ. After the operator presses
the READ key, either CF: UNCORR or CF: CORR, followed by LOCAL DENS, will be displayed during the
measurement period if the TemProbe is being used. If the TemProbe is not being used, the standard temperature
(70
/ F or 21.1/ C) will be displayed following LOCAL DENS. Each subsequent air flow measurement is triggered
by pressing the READ key.
Place the FlowHood over the outlet (or inlet) diffuser or grille, so as to capture and direct the air flow through the
FlowHood base. The foam gasket around the edge of the top assembly should be firmly pressed against the
ceiling or the edges of the diffuser. Air flow through the unit should not be blocked or influenced by any object
within one foot of the FlowHood base. The unit should be supported with both hands, one on the handle, and
the other at any convenient point on the outside of the base. Set the flaps control knob to the open position.
Press the READ key or the thumbswitch on the FlowHood handle and the reading will be displayed directly in cfm
or liters/sec. A negative number indicates that the air flow is being exhausted through a return outlet. A second
reading with the flaps closed will be necessary to determine the actual air flow.
SAFETY NOTICE
When using the FlowHood to test air flow at ceiling outlets, be sure that you can safely raise
and support the unit during the measurement. This is especially important when working on
a ladder.
11.1 AIR FLOW - NONBACKPRESSURE COMPENSATED READINGS
See Section 9.2 BACKPRESSURE COMPENSATION for a general discussion of backpressure and its effect on
any capture hood device before using the FlowHood for nonbackpressure compensated readings. This technique
measures air flow without compensating for FlowHood induced backpressure. This method may be used for
both supply and return outlets.
After the meter and all of its connections have been attached to the FlowHood, as described previously, set the
flaps control knob to the open position. Place the FlowHood over the outlet (or inlet) diffuser or grille. Wait two
or three seconds to allow the air flow to stabilize, and then press the READ key or the thumbswitch on the
FlowHood handle. The displayed result will represent the flow value of the outlet while the FlowHood is in place.
This flow reading will generally be somewhat less than the actual flow, due to the backpressure effect of the
FlowHood.
11.2 AIR FLOW - BACKPRESSURE COMPENSATED READINGS
Air flow through an outlet (or inlet) is reduced to some degree by any capture hood device placed over the
opening. Correction curves had traditionally been used to provide an average correction factor for the
backpressure effects at different air flows.
This method measures air flow with compensation for the FlowHood induced backpressure automatically
calculated into the displayed result. Backpressure compensation requires two readings in immediate sequence.
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